docs: def _find_aux_coord_vars(self, ds, refresh=False):
          '''
          Returns a list of auxiliary coordinate variables
  
          An auxiliary coordinate variable is any netCDF variable that contains
          coordinate data, but is not a coordinate variable (in the sense of the term
          defined by CF).
  
          :param netCDF4.Dataset ds: An open netCDF dataset
          :param bool refresh: if refresh is set to True, the cache is
                               invalidated.
          :rtype: list
          :return: List of variable names (str) that are defined to be auxiliary
                   coordinate variables.
          '''
          if self._aux_coords.get(ds, None) and refresh is False:
              return self._aux_coords[ds]
  
          self._aux_coords[ds] = cfutil.get_auxiliary_coordinate_variables(ds)
          return self._aux_coords[ds]